Answer: I think the potting soil you have chosen is just fine for your new corn plant. When you find brown spots ringed with yellow on the leaves, it indicates a wound to the leaf tissue. This can be caused by handling, by insect feeding or even by a disease pathogen. The injury becomes brown as the plant tries to seal off the wound and the yellowing indicates additional dying tissue. You will need to look closely at the brown/yellow spots to determine whether there is insect activity. At this point I would simply wipe each of the leaves off with a dampened paper towel. If there are insects, you will wipe them off. Watch your plant for additional leaf spots. I suspect you wont' see any more develop.
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